The present invention relates to improvements in paper making machines, and more particularly to an improved headbox for supplying paper stock from a supply conduit from a fan pump and distributing the stock across the width of a machine to a slice chamber.
In the formation of a traveling fibrous web by depositing fibers in a slurry onto a porous forming surface, the stock is distributed onto the surface from a slice chamber through a slice opening. In order to maintain uniform velocity of flow and fine scale turbulence in the stock, it is fed into the slice chamber through a plurality of tubes forming a tube bank with the tubes essentially uniformly distributed across the machine. In one form of such construction for compactness, the unit is arranged so that the distributor tube bank feeds downwardly directly into the slice chamber and the tube bank is conventionally supplied with stock from a header extending across the machine positioned above the tube bank. To maintain a uniform velocity of flow of stock across the header, the stock is supplied to the header from a conduit leading from a fan pump at one side of the machine and the header tapers to a small end at the other side of the machine and excess stock may flow through a recirculating line leading off from the small end of the header. In this arrangement in order to maintain the distributor tubes at a uniform length, the top wall of the header chamber slopes in a downward direction. The downwardly sloping wall of the header chamber tends to cause air bubbles to form and tends to cause the fibers of the stock to gather along a wall. Also, the fibers will tend to conglomerate and nonuniform flow will result so that the stock gets dirty as these conglomerates of fibers are released and flow further along the header or down through the distributor tubes. Such dirty stock or conglomeration of fibers will cause marked defects in the resultant paper. That is, in order to produce uniform paper, the stock must continue to flow uniformly at all locations and cannot slow down, the fibers cannot conglomerate and air bubbles cannot be permitted to form.
A feature of the present invention is to provide an improved headbox arrangement where the advantages of a compact tube bank which leads immediately directly down into the slice chamber are retained, yet the disadvantages of stock defects and gathering air bubbles are avoided.
It is accordingly an object of the present invention to provide an improved headbox construction with a tube bank leading downwardly into a slice chamber and a header chamber for supplying stock to the tube bank wherein the header chamber does not have any downwardly sloping surface.
A still further object of the invention is to provide an improved headbox construction of the type described with improved clean-out features wherein easy and immediate access to the header chamber and tube bank is readily afforded.
A still further object of the invention is to provide an improved headbox construction with a unique cover arrangement which forms a chamber wall for the distributor tube bank and the header chamber.